1. Field of the Invention
Embodiments of the present invention generally relate to a variable capacitor for radio frequency (RF) and microwave applications.
2. Description of the Related Art
As the size of semiconductors continues to shrink, so does the micro-electromechanical systems (MEMS) that are coupled to the semiconductors. MEMS devices may be used in miniature relay switches, capacitive switches, non-volatile memory elements and for many more applications. The MEMS devices have a suspended structure that moves between at least two positions to modify the electrical impedance to the flow of continuous or alternate current
MEMS devices are made using similar processing steps to those found in semiconductor foundries and therefore can be manufactured cost effectively on a wafer scale. Some of the issues that arise in MEMS devices include unwanted capacitive coupling, series inductance and losses. To minimize unwanted capacitive coupling, high quality substrates, such as sapphire or quartz, have been considered with heterogeneous integration of semiconductor processes thereover. Another technique to minimize unwanted capacitive coupling is to increase the size of the intrinsic MEMS device, e.g., the variable capacitor, in order to minimize the relative impact of stray capacitance on the device performance (i.e., the capacitance tuning ratio).
Large cross section interconnects have been used to attempt to minimize series inductance and losses and therefore to maximize the quality factor. High conductivity metallizations has also been attempted to maximize the quality factor. Additionally, minimizing losses due to packaging by adopting chip level assembly integration strategies and the use of high quality low loss substrate materials such as sapphire and quartz have been attempted in order to maximize the quality factor.
To date, the efforts to minimize capacitive coupling, minimize series resistance and inductance, and therefore maximize the quality factor have not been as successful as desired. Therefore, there is a need in the art for a MEMS variable capacitor that minimizes unwanted capacitive coupling, minimizes series inductance and maximizes the quality factor.